Two new spontaneous guinea pig models, the L76 leukemia and mammary carcinoma, are under investigation in support of the common antigen and immunotherapy studies. The L76 leukemia exhibited a striking hematological and pathological similarity to acute monocytic leukemia in man. Treatment of leukemic pigs with either one administration of 100 mg/kg of cytoxan or 2 courses of the drug at lower doses over a 2 week period gave a similar suppression of the disease for a 5 week period before relapse and death of 98% of the treated animals. Surgical removal of the spontaneous mammary tumor (15-20 mm) alone or followed by cytoxan therapy resulted in metastasis only to the lungs. In vitro and in vivo testing for drug suppression against the L2C and L76 leukemias has shown the animals to be immunologically competent one week after drug therapy. A combined modality approach utilizing chemotherapy, surgery, immune-stimulators (C. parvum and glucan) and vaccines alone or in combination is being applied to the L2C and L76 leukemias and the spontaneous mammary carcinoma in guinea pigs. BIBLIOGRAPHIC REFERENCES: Klein, D. and Pearson, J.W.: Modulation of host immune response against the L2C guinea pig leukemia. Fed. Proc. (In press, 1977). Schlom, J., Michalides, R., Perk, J., Pearson, J.W. and Dahlberg, J.: Biochemical properties of the B-type retravirus of guinea pig and an agent in the plasma of guinea pigs with L2C leukemia. Fed. Proc. (In press, 1977).